This invention relates to a gas bearing and more particularly, a hydrostatic and hybrid gas bearing utilizing a hydrostatic effect and a hydrodynamic effect and being capable of efficiently operating with a small bearing clearance of less than 10 microns.
Such a bearing is indispensable for high speed operation of a mass storage memory device utilizing a rotating head recording device. The rotating head recording device is more advantageous than the prior art fixed head magnetic tape recording device in that it can record at a high recording density and it can decrease the size of the recording device. But it has such defects that its data transfer rate is low and sequential access time is long. This is because the rotating speed of the presently available rotating head is 5600 r.p.m. and the head scanning speed is also low, for example, 25.4 m/s. If one succeeds in increasing the rotating speed to about 15,000 r.p.m. and the head scanning speed to about 50 m/s, the problems described above can be eliminated. Increase of the speed above 10,000 r.p.m. is impossible with a ball bearing because of its poor reliability so that it is essential to use an air bearing.
The rotating head recording device utilizing a hydrostatic type and/or hydrodynamic type air bearing is now being used for broadcasting VTR. However, the hydrostatic type air bearing requires a reciprocating compressor so that it is difficult to adapt such a recording device to the computer peripheral equipment. On the other hand, in the hydrodynamic type air bearing, since the shaft and bearing are in contact with each other before starting, it lacks reliability when used in the rotating head recording device for electronic computers which are required to operate for several years without resort to any maintenance or repairs. Accordingly, it has been desired to provide a hybrid gas bearing (that is a bearing which supports the shaft by hydrostatic pressure at the time of starting and stopping, whereas by the hydrodynamic pressure during rotating) that can operate with high efficiencies by using pressurized air having a pressure of about 0.08 kg/cm.sup.2 created by a conventional blower, in order that a highly reliable, high speed rotating head recording device which can start and stop in a contactless condition can be obtained.
Prior to this invention, to operate a hydrostatic gas bearing of so-called inherent restrictor type, it has been necessary to use a reciprocating compressor as has been pointed out above because the bearing efficiency (the ratio between supplied air pressure and pressure available to support a shaft) is low, for example, about 50% at the most. In addition, since the optimum bearing clearance is large, the bearing stiffness (bearing efficiency/bearing clearance) is small. In other words, in the conventional bearing, it has been impossible to decrease the optimum bearing clearance below 10 microns without appreciably decreasing the bearing efficiency. For this reason, in the bearing of this type, it has been impossible not only to sufficiently increase the bearing stiffness but also to effectively utilize the hydrodynamic effect created in a small bearing clearance at the time of high speed running for the sake of effectively operating the bearing as a hybrid gas bearing.
In order to eliminate at least a portion of the defect of the inherent restrictor type bearing, a surface restrictor type bearing has been proposed in which the optimum bearing clearance was reduced in less than 10 microns, and a bearing pressure for supporting a load is effectively created in a region including the bearing ends providing a bearing efficiency substantially equal to that of the inherent restrictor type bearing and a higher bearing stiffness. However, the surface restrictor type bearing must be provided with many longitudinal axial slots which are difficult to machine. Moreover, as such longitudinal slots make discontinuous the bearing surface in the relative slip direction, this prevents effective use of the hydrodynamic effect created by the rotation of the shaft so that this type of bearing can not operate as a hybrid gas bearing.